3.2. COMPARING THINGS 19
Subtraction and division of numb e r s follow t he same rules as addition. However, these operators, as defined,
do not work for strings and arrays.
Of special note is the division operator with respect to integer operands. Consider evaluating the fol l owing
expression:
15 / 2
If one asked the Python i nterpreter to perfor m this task, the result would be 7.5, as expected. However,
often we w is h for just the quotient without the remainder. In this case, the qu ot ie nt is 7 and the remainder
is 0.5. The double forward slash ope r ator is P y th on ’s quotient operator; if we ask the interpreter to evaluate
14 // 5
the resu l t would be 2, not 2.8. Use of the quotient operator is known as integer division.
2
The complement to integer division is the modul us operator %. While the result of integer division is the
quotient, the res ul t of the modulus operator is the remainder. Thus
14 % 5
evaluates to 4 si n ce 4 is left over when 5 is divided into 14. To check if this is true, one can ask the interpreter
to evalu at e:
(14 // 5 * 5) + (14 % 5) == 14
This complicated expression asks the question “is it true that the quotient times the divisor plus the remainder
is equal to the original divi d en d? ”. The Python interpreter will respond that, indeed, it is true. The reason
for th e parentheses is delineate the quotient and the remainder within the addition. The parentheses can
also be used to change the precedence of operat or s; this is is explained in more detail in the next chapter.
3.2 Comparing thi ngs
Remember the Boolean literals, True and False? We can use the Boolean comparison oper at or s to
generate s uch values. For example , we can ask if 3 is l e s s than 4:
>>> 3 < 4
True
The interpreters re sponse says that, indeed, 3 is less than 4. If it were not, the interpreter would re spond
with False.Besides< (less than), there are other Boolean comparison operators: <= (less than or equal
to), > (greater than), >= (greater than or equal to), == (equal to), and != (not equal to).
Note that two equal signs are used to see if to things are the same. A single equals sign is reserved for the
assignment operator, which you will learn about in a later chapter.
Besides integers, we can compare reals with reals, strings with strings, and arrays with arrays using the
comparison operators:
2
In most other modern programming languages, a single / means integer division, so don’t forget this when you learn a new
language!
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